Propeller pitch lock



March 1, 1955 D. R. PEARL PROPELLER FITCH Loox 2 Sheets-Sheet 1 FiledMarch 6, 1952 March l, 1955 D. R. PEARL PROPELLER FITCH LOCK Filed March1952 2 Sheets-Sheet 2 NNN ms QSA, E

United States Patent() f"ce PROPELLER PITCH LOCK David R. Pearl, WestHartford, Conn., assignor to IUnited Aircraft Corporation, EastHartford, Conn., a corporation of Delaware Application March 6, 1952,Serial No. 275,051

3 Claims. (Cl. 170-160.32)

This invention relates to variable pitch propellers `and moreparticularly to propellers having positive blade pitch locks.

It is an object of this invention to provide a variable pitch propellerhaving a positive pitch lock for preventing blade pitch variation undercertain conditions.

It is a further object of this'invention to provide a pitch lock for avariable pitch propeller wherein the pitch lock mechanism responds tothe speed of rotation of the propeller to lock the blades against pitchchanging movement. i

It is another object of this invention to provide a pitch lock of thetype described which responds to a pressure loss in the systems of ahydraulically actuated Variable pitch propeller and is responsive to therelative positlon of the pitch control for the propeller blades.

These and other objects of this invention will become readily apparentfrom the following description of the drawings in which:

Fig. 1 is a longitudinal section through a propeller and its pitchchanging mechanism mounted on a drive shaft.

Fig. 2,is a detail cross-sectional View taken along the line 2-2 of Fig.1

Fig. 3 is a cross-sectional view taken along line 3-3 of Fig.v l.

Fig. 4 is a schematic diagram of the propeller pitch changing systemincluding means for actuating a pitch lock; and A Fig. 5 is across-sectional and schematic view of a manually operated system forengaging the pitch lock.V

The propeller shown in Fig. l comprises a hub secured on shaft 12 (whichmay be a part of thefengine crankshaft or-a separate propeller shaft)and retained in position thereon by the usual cones 14 and retaining nut16. The cones 14 are of the split type to permit installation. Hub 10carries a plurality of blades 18, three in the modification shown,mounted for pitch changing movement on bearings 20 in hub socket 22.Each blade 18 is providedwith a gear segment 24 which meshes with commongear 26 for simultaneously turning all the blades to vary their pitch.Gear 26 is actuated by and may be integral with a cam 28 which is turnedby the action of cam followers 30 movable by a piston 32 and cooperatingwithboth cam 28 and a iixed cam 34. For a more detailed descriptionofthe cam and cam followers reference may be made to Caldwell et al.Patent No. 2,174,717 or Martin et al. Patent No. 2,280,713.

Piston 32 is slidable, by a preponderance of oil under pressure on oneside or the other, in a cylinder formed by dome 36. Piston 32 is in theform of an annulus and, in the center, slides over a sleeve 38 thepurpose of which is described in copending patent application Serial No.193,481, filed November l, 1950. Piston 32 is shown as sealed at thecylinder and at the sleeve by O-ring seals 31 and piston ring 33respectively.. The ring 33 is carried by sleeve 38 and engages sleeve 35which is fixed to and axially movable with the piston 32. From the abovedescription it is apparentthat a preponderance of oil pressure on eitherside of piston 32 will move the piston and cause a change in the pitchof the propeller blades.

Oil is conducted from a governor described hereinafter and which isdriven in timed relation to said propeller, and piston 32 through twolines 42 and 44. The governor acts to selectively increase theV pressurein one line and reduce the pressure in the other in order to move thepiston 32 and control the propeller pitch to maintain constant speed.

- In order to move the piston in an inboard direction,

yfront or outboard side of piston 32. The oil under pressure ows fromline 42 and channel 46 through the shaft splines 51, the split in cone14 and inally iinds its way to channel 47 and passage 49.

Oil under pressure in line 44 finds its way internally of the hub to theaft or inboard side of the piston 32 tending to force the piston forwardor outboard. When the governor introduces fluid through line 42 andchannel 46 the front side of piston 32 is connected via line 44 to drainor sump.

The chamber 48 has a passage 54 which communicates with the top side ofa centrifugally operated check valve 56 (also seen in Fig. 2). Theunderside of valve 56 as viewed in Figs. l and 2 communicates with adrilled passage 58 which connects with line 59 leading to theatmospheric sump as indicated in Fig. 1 and as fully described inconnection with Fig. 4.

As seen in Fig. 1, a pitch lock oil line 70 is'provided whichcommunicates with a passage 72 in the propeller hub 10. The passage 72communicates with a chamber 74 in the hub 10. When pressure is suppliedto the chamber 74 an annular ring or lock element 76 is forced inboardor to the right, as viewed in Fig. l, against the force of a pluralityof springs 78. The lock element 76 is splined to the hub so thatalthough it is permitted to move along the axis of propeller rotation itis txed for rotation with the propeller and hub 10. A second lockelement 80 is fixed to the blade interconnecting gear 26 and also to therotating cam portion 28 of the pitch changing mechanism. The pitch lockelements 76 and 80 are more clearly seen in Fig. 3. The adjacent facesof the pitch lock elements 76 and 80 have engageable teeth 84 which asshown are constructed to permit relative movement in one direction butto prevent relative movement in another direction when the teeth areengaged. Thus, when the teeth 84 are engaged it is desirable to preventblade pitch change in a lowpitch direction only.

Each of the pitch lock elements 76 and 80 include cooperating camelements 86 and 88, respectively, as shown in Figs. 1 and 3. Thesecooperating cam lelements positively disengage the pitch lock elements76 and 80 in certain pitch range positions of the blades, as for examplein the feathering and reversing ranges.

Thus, from the foregoing it is seen that by providing oil under pressureto the chamber 74 the pitch lock elements 76 and 80 will be disengagedand that in certain ranges even in the absence of the pitch lock oil inchamber 74 the pitch lock will be positively disengaged.

A pitch changing system and the pitch lock control is schematicallyillustrated in Fig. 4 where like numerals are utilized to indicate likeparts shown in the previous figures.

As shown herein, a sump is under atmospheric pressure and containsfluid'which is withdrawn therefrom by a scavenging pump 102 which inturn supplies the main sump 104 with fluid under pressure. The main sumpis maintained at some pressure higher than atmospheric by means of arelief valve 106.' The propeller control system is supplied with uidunder pressure from the main sump by means of a main pump 108-and anauxiliary pump 110. The usual relief valve and check valves areillustrated. The main pump 108 supplies uid under pressure to a manifold116 which in turn connects tovarious portions of the hydraulic system.Primarily, the manifold 116 leads to a line 118 in the body of the valve120. The movable portion 122 of the vValve includes a plurality of landswhich control the liow of fluid to the propeler pitchA changingmechanism and to the pitch lock. Thus, for example, when the governor126 moves the valve portion 122 upwardly,

high pressure fluid is supplied to the line 142 to the high pitch sideof the piston 32. Likewise, when the governor low pitch valve`132includes a movable piston 134 which Patented Mar. 1, 1955 p sage144`andtheninto the `line-44 'and' to thelow pitch` side" ofthe pistonA32. When th'epistonu 134 of 4the -low' pitchV valve 132 is movedtotheright it blocks ofi the line 140 leading to the mainl sump:

The pitch lock valve 130 insuresthat there'is adequateV pressure in thepitch lock. actuating` system to hold the pitch lock unlockedbeforetluid is permitted to ow to the low pitch side of thepitchrchangingY piston 32. The lowpressure relief valve 150is'provide'din the system so thatthe mainpump supplies'arpressureonlyhigh enouhg to hold the desired blade pitch and hence at 4less than mainpumprelief pressure. The valve 150 is not fundamental to the pitch',lock but-since'in normal operation the excess or waste ilow of'thelmain-pump Vis flowing through the valve, such flow is utilized as asource of supply for the pressure required toy hold the pitch lock in anunlocked position.

Actually then the pitch lock valve v130 acts as a relief valve for theexhaust ow from valve 150 and by virtue of spring 164 the pressure-in160 .is at aspredetermined pressure which is higher than main sumppressure. This uid under pressure in 160l also ows through passages 170,172, 70 and to 74 to hold the-pitchl locknormally unlocked.

The oil under pressure in chamber 160 has three possible sources. Theseinclude the by-pass oil'from low pressure relief valve '0, the oilcoming from the high pitch line check valve 161, and oil directly fromthe main pump 108 through line 200 and passage 201. The length of thepitch lock valve piston 162 from its bottom surface up to the lower edgeof the annulus 202 is of controlling importance since the normal supplyof oil to chamber 160 comes through passage 200 and is metered toannulus 202 and passage 201 in such quantityl as is necessary tomaintain the required pressure in chamber 160. The pressure in 160y(excepting in some extreme conditions such as unfeathering at50,000--ft. altitude) is maintained at a constant value above mainsumppressure. The elevated pressure above sump pressure is maintained asfollows. Main sump pressure is applied to the top end of pitch lockvalve piston 162 and the force of the spring 164 is added to theforceexerted by themain sump pressure. These forces must then bebalanced by a pressure higher than main sump pressure (in chamber 60) so.as to .maintain avalve piston position such that line 128 willbeincommunication with line 203.

The same applies for an unfeathering operation after the blades are backout of the operative range of the kick-out cam 86.

For normal operation in the governing range of blade angles valveelement 162 of valve 130 is in theY -position shown in Fig. 4 so thatthe blades can be moved to low pitch by pressure moving to line 44. Thenormal governing of the system moves theblades to low pitch by reducingpressure in line 42 vsomewhat and allowing Vcentrifilgal vtwistingmoment to carry the blades 4toward'low pitc To feather` the propellerthe feathering solenoidvalve` hydraulically moves governor. valveelement 122, up. This causes the pitch lock to become Vengaged but hereagain the ratchet teeth permit pitch change toward high pitch until thepitch lock kick-out cam range is reached.

Under normal operating conditions the line 140 is connected to the mainor pressurized sump 104 and hence likewise line 168. Chamber 160 is alsoconnected to the main sump by reason of the piston 162 uncovering asmall portion ofthe lowermost port leading to line 168.

Under., such ,conditions then .the line -170 isalsogunder;

mainzsump pressure and provides. fluid under thispressure to the port172 of the control valve 122. Thus, as illustrated, the movable valveportion 122 includes an additional land 176 which normally suppliesfluid from the port 172 to the line 70 leading to the chamber 74 of thepitch lock. In the valve position illustrated, pressure from chamber 160of pitch lock valve `130 is supplied (via lines 170, 70) to the chamber74 of the pitch lock so that the movableelement 76-of the pitch. lock isheld disengaged from the element 80 of the pitch lock.

During a predetermined overspeed condition, i. e., when the land 176 vofthe valve 122 moves upwardly a predetermined amount, the pitch lock line70 will be disconnected from 172 and will be connected to the line 180which leads to the atmospheric sump. Thus under these conditions thechamber 74 of the pitch lock will be connected to the atmosphere so thatthe springs 78 of the pitch lock will move the element 76 intoengagement with the lock element 80 to prevent pitch changing movementto lower pitch.

The ratchet type teeth are provided on the pitch lock elements so thatythe normal hydraulic system may function to move the blades toward highpitch and thus correct an overspeed condition, or to feather thepropeller if the operator desires, even though the pitch lock is in thelocked position whether manually or automatically.

In the event that it is desirable to include a manual as well asautomatic controlV for the pitch lock, a valve such as illustrated inFig. 5 may be connected in thepitch lock line 170, as illustrated inFig. 4. ln the normal position of the manual pitch lock valve 220 itmerely supplies the path from line to port 172 of the governor valve sothat thefpitch lock may function automatically in response to speed orlow pressure. With the manual pitch energized by means of switch 224 theelement 202 moves to the dotted position so that the valve disconnects'170 from 172 and connects 100 to 172 so that the cham-A pitch changingmechanisrnand the pitch lock are located in the propeller hub it is.desirable to keep these units filled with oil. Therefore, when thepropeller stops rotating the valve 56 will close oifA the line 54 toprevent draining all the oil from the hub back to the atmospheric sump.When the speed of the propeller is sufficient and fluidis being suppliedfrom the main pump, the centrifugal valve. then opens to permit anydrainage that may be necessary.

The remaining elements illustrated in Fig. 4 do not form a specific partof this invention and hence theV description thereof is omitted hereinfor convenience.

As a result of this invention it is readily apparent that a simple yeteiiicient pitch lock mechanism is provided which responds to apredetermined position of the control valve 122 relative to the valvebody 120. In other words, the pitch lock control is a speed responsivedevice.

`Although only one embodiment of this invention has been illustrated anddescribed herein, it will be apparent `that various changes andmodications may be made in the construction and arrangement of thevarious parts without departing from the scope of this novel concept.

What it is desired to obtain by Letters Patent is:

l. In a lock for thepitch changing mechanism of a controllable pitchpropeller having a hub, said propeller having variable pitch blades andcontrol mechanism therefor, said control mechanism being movable in twodirections, lock means interconnecting the pitch changing mechanismandthe hub including a single acting servo for engaging and disengagingsaid lock means, means tixedrelative to said control mechanism,meansresponsive.V to predetermined positions between said controlmechanism and said fixed means operatively connected tosaid servoy forcontrolling4 the engagementl and dis-A engagement of said lock means,and manual means operatively connected to said servo for overriding saidlast pressure, speed responsive means for controlling saidfA pitchvvarying means including opera-tive connections to said pitch varyingmeans and said source, blade lock means interconnecting the pitchchanging mechanism and hub, means holding Asaid lock in an'unlockposition includmg a p1ston engageable with said blades,`aspring-engaging -oneside o'fsaid pistonandfurging -said piston into.blade lock position, the spring side of said piston beingf,

vented to atmosphere, means for admitting fluid under pressure to theother side of said piston to maintain the llatter in an unlock position,means fixed relative to said control means, means responsive to apredetermined relationship between said control means and said fixedmeans including a movable valve having a land for connecting said otherside of said piston to atmosphere upon a predetermined movement thereofin one direction, and manual means operatively connected to said pistonfor overriding said relationship responsive means and connecting theother side of said piston to atmosphere for engaging said lockirrespective of the relationship of said control means and said xedmeans.

3. -In a propeller having a hub, a plurality of blades mounted for pitchchanging movement in said hub, means `for varying the pitch of saidblades including a source of. uid under pressure, means for controllingsaid pitch varying means including a valve movable in pitch increasingand decreasing d-irections and operatively connected between said sourceand said pitch varying means, a pitch lock comprising engageable lockelements operatively connected to said hub and blades respectively forlocking said blades against movement, said lock including cooperatingca-m members engageable in predetermined blade pitch ranges forpositively unlocking said lock elements, a piston connected to one ofsaid elements for engaging said one element with the other element, acompression spring engaging one side of said piston and urging saidpiston toward a pitch lock position, a land forming a portion of saidvalve for directing fluid under pressure to the other side of saidpiston to disengage said elemen-ts, means cooperating with said land forconnecting said other side of said piston to drain irrespective of theposition of said blades, said land connecting said other side of saidpiston to drain in response to a predetermined movement of said valve ina pitch increasing direction, and a port `fixed relative to said landfor establishing the amount of said predetermined movement includingoperative connections to the other side of said piston.

References Cited in the file of this patent UNITED STATES PATENTS2,174,717 Caldwell et al. Oct. 3, 1939 2,280,713 Mart-in et al Apr. 21,1942 2,282,297 Keller May 5, 1942 2,320,195 Rindfleisch May 25, 19432,343,416 Keller Mar. 7, `1944 2,392,364 Caldwell et al Jan. 8, 19462,477,868 Forman Aug. 2, -1949 2,592,124 Diefenderfer Apr. 8, 19522,635,702 Anderson Apr. 21, 1953 2,653,671 Martin et al Sept. 29, 1953

